The present invention relates to an electric discharge recording material, more particularly to an improved electric discharge recording material by using aggregated carbonblack particles.
Conventionally, it has been known that this kind of electric discharge recording materials have various kinds of disadvantages. For example, the well known electric discharge recording materials having exposed, deposited metal layer has the following disadvantages:
(1) the surface layer has high metallic luster and the contrast between a recorded image area and the non-imaged area is low, since the surface layer consists of a deposited metal layer and therefore, the image is not clear; PA1 (2) the writing property is not good; PA1 (3) since the surface is relatively smooth, the contact resistance between the layer recorded and the recording needle is very low, the large amount of current is instantaneously passed through when the electric potential is applied therebetween, this leads to a severe destruction of the layer to be recorded, and thereby the reproducibility of the dots becomes bad and the printing image is inferior in its sharpness and becomes unclear. PA1 (4) a potential difference is caused between the carbonblack particles and the deposited metal layer, due to the conductiveness of the carbonblack contained in the colored layer, the potential difference causing an electrochemical corrosion of the deposited metal, in other words such discharge recording material has low shelf stability, while the corrosion is advanced more and more, the original conductivity of the deposited metal layer decreases and therefore, bad recording is resulted. PA1 (5) similar to the said item 4, the corrosion of the deposited metal layer is caused, thereby unsatisfactory results are obtained, such as bad appearance, poor recording property etc.
In order to overcome these disadvantages, it is also well known that a protective layer has been applied on the deposited metal layer. However, in such electric discharge recording material having the protective layer, the following disadvantages are resulted in:
In order to solve said disadvantages particularly the problem of the shelf stability, Japanese Laid-Open No. 63948/1975 discloses a method in which the colored layer of the discharge recording material is constituted from carbonblack and a resin and the surface electrical resistance of said colored layer is confined to a range of 10.sup.8 to 10.sup.11 .OMEGA./cm.sup.2. However, if the colored layer is highly insulated state, this causes disadvantages such that the spark noise due to discharge is significant and the sharpness of the edges of the printing image is bad. In addition, problems such that the leak of discharge is caused on the return electrode and thereby the drawing of an image becomes impossible are caused since a significantly large load is subjected to the deposited metal layer.
Under such circumstances, Japanese Patent Publication No. 15416/1979 teaches the use of a carbonblack graft polymer as a pigment and Japanese Laid-Open No. 73145 teaches the use of a barrier layer between the colored layer and the deposited layer in order to improve said disadvantages.
Furthermore, the process which comprises incorporating an organic or inorganic pigment such as silica, alumina to the colored layer to roughen the surface of the colored layer and thereby pseudo-whitening the surface, is disclosed in Japanese Laid-Open No. 38551/1975. However, in this process, the following disadvantages are resulted owing to the use of the generally broad size distribution of the pigment to be incorporated; the surface roughness of the recording layer becomes too large, and the dots resulting from discharge are likely to be nonuniform. Moreover, discharge on the return electrode is likely to be caused. This is because the deposited layer is destroyed by the increased current density on the return electrode at the time of recording due to considerably high contact resistance between the return electrode and the recording layer. In addition, depending on the chemical and physical properties of the pigment used for roughening the surface of the metal layer, it is observed that the corrosion of the deposited metal layer is accelerated, scanning line of the recording needle become more remarkable and the like.